Along with the recent rapid increase in the use of smartphones, various attempts have been made to develop a mutual control method between a smartphone and a peripheral device. In particular, research into a smart watch in which a smartphone and a watch are combined has been actively conducted, and some prototypes have been commercialized. A smart watch is used to control or monitor functions of a smartphone, such as calling, messaging, and usage of an application. The smart watch consumes more power than a general wrist watch, and thus there is a problem in that the smart watch should be frequently charged or have a large-capacity battery to continuously supply power thereto.